In order to increase the number of payloads that can be flown with reduced costs, spacecraft have been modified to work as a platform on which another or secondary payload can achieve access to space. The secondary payload may be a micro-satellite or a collection of sensors, electrical units, and antenna. There are two primary ways to accomplish this task, integrating the payload into the parent satellite or integrating the payload onto the parent satellite. One approach to integrating the payload into the parent satellite includes installation of the payload hardware during the manufacturing of the spacecraft. Units are mounted directly on internal equipment shelves and spacecraft subsystems are redesigned to accommodate the specific needs of the hosted hardware.
Another approach involves mounting a hosted payload onto the spacecraft. For example, small satellites intended to be launched as secondary, ride-share payloads may be mounted to Evolved Expendable Launch Vehicle (EELV) Secondary Payload Adapters (ESPAs). ESPAs are formed as a ring structure that include a plurality of circular ports formed at intervals around the ring for mounting smaller satellite components on the exterior of the ring. ESPAs are designed to mount to the launch stack of an EELV (typically, below the primary payload that is mounted in the EELV with a primary payload adapter). Upon deployment from the launch vehicle, the satellite components are separated from the ring structure of the ESPA. Other recent designs, such as the Demonstration and Science Experiments (DSX) Satellite and Lunar Crater Observation and Sensing Satellite (LCROSS), use the entire ESPA ring as part of the satellite structure, thereby using the multiple payload ports to attach the various satellite components. For these designs, the satellite components are retained on the outer surface of the ESPA ring in order to form a satellite that uses the entire ESPA ring and exterior components mounted to the outside of the ESPA ring as part of its structure.